This study investigated the incidence of a microdeletion of the 22nd chromosome in patients with familial congenital heart disease. Study participants were recruited from a group of individuals who had a corrective operation for tetraology of Fallot at the University of Minnesota between 1954 and 1974. All patients with tetralogy of Fallot and immediate family members with tetralogy of Fallot or related heart defects were invited to participate. While at the GCRC, the study protocol was discussed with each participant and blood collected for cytogenetic analysis.